Voice modulation recognition in a radio-to-sip adapter

ABSTRACT

A radio-to-SIP adapter is shown to include a voice detection algorithm processor as well as other circuitry to provide an interface between a radio and SIP adapter to accommodate a transition from half duplex to full duplex and to cause a radio to transmit when human speech is present in an audio signal from a telephony network.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority under 35 U.S.C. § 119(e) from U.S.provisional application No. 60/835,568 filed on Aug. 4, 2006.

FIELD OF THE INVENTION

This invention relates generally to hand held radio equipment and moreparticularly to systems and techniques to interface such hand-held radioequipment to telephony networks.

BACKGROUND OF THE INVENTION

Hand-held radio equipment is often used in public safety and during anemergency it uis often desirable to connect the hand-held radio to atelephone network. In recent times, telephone networks are implementinga new communication technique commonly referred to as Voice over IP,where voice communication is communicated using an Internet Protocol(IP) network. The Voice over IP community has adopted Session InitiationProtocol (SIP) as a protocol of choice for signaling. SIP is a signalingprotocol used for establishing sessions in an IP network and is an RFCstandard (RFC 3261) understood by those skilled in the art. Using SIP,telephony becomes another web application and integrates with otherInternet services.

In public safety applications, it is often desirable to interfacehand-held radio equipment to a telephony network through a so calledRadio-to-SIP adapter. Such hand-held radio equipment which typicallyoperate in half-duplex lacks a means of being controlled by the callsthrough the SIP network without requiring operator intervention of sometype.

It is desirable to provide a technique where radio calls from thenetwork using SIP can control the activation of the radio transceiverswitching the transceiver from receive to transmit and back to receiveagain when the party on the telephony network wishes to speak.

SUMMARY OF THE INVENTION

In accordance with the present invention, a radio-to-SIP adapterincludes a voice detection algorithm processor to detect the presence ofhuman speech in an audio signal; an audio input to receive an audiosignal; and a radio transmit indicator signal output to provide a signalto indicate that human speech is present in the audio signal. With suchan arrangement, radio calls can be initiated by the telephony networkusing SIP without requiring operator intervention.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing features of this invention, as well as the inventionitself, may be more fully understood from the following description ofthe drawings in which:

FIG. 1 is a block diagram of a voice modulation recognition radio-to-SIPadapter according to the invention;

FIG. 2 is a flow chart showing the operation of the radio-to-SIP adapteraccording to the invention; and

FIG. 3 is a block diagram of a voice detection algorithm implemented insoftware according to the invention.

DETAILED DESCRIPTION OF THE INVENTION

One familiar with hand-held radios will appreciate that in normaloperation the radio operates in what is known as half duplex mode wherea receive signal is received through the receiver and an audio output isprovided by the speaker to an user. When the user wishes to talk, apush-to-talk button is depressed which activates the transmitter and theuser speaks into the microphone to transmit. For ease of operation, mosthand-held radios provide an external microphone and speaker interface sothat an external microphone and speaker headset can be used. A basestation is similar to a hand-held radio except being configured for amore permanent location. In a typical operation, a plurality ofhand-held radios will communicate among each other and with a basestation.

When a radio transceiver, which is half-duplex in nature, is interfacedto a SIP (Session Initiation Protocol) telephony network, which isfull-duplex in nature, the need exists to control the activation of thetransmitter, switching it from receive to transmit and back again whenthe party on the telephony network wishes to speak. By analyzing theaudio from the telephony network and using an appropriate signalprocessing algorithm the determination of the existence of human speechenergy can be made and a transmitter can controlled efficiently.Existing systems use an absolute level sensing system referred to as VOX(voice operated switching) which does not examine the content of theaudio. Background noise and non-speech signals can “false” theactivation of the transmitter. Other methods involve designating a keyon a telephone keypad as a “push-to-talk” (PTT) button, but thisrequires user training and is prone to error.

In the present invention, a radio is activated when the user of the SIPtelephony device speaks, but is not activated by background noise orother non-speech signals. This provides a reliable and transparentconversion from a half-duplex radio system to a full-duplex SIPtelephony network. The present invention allows radio transceivers to beconnected to a telephony network via SIP (Session Initiation Protocol).One problem with such an interface is the disparity between thehalf-duplex nature of the radio (one may transmit or receive, but notboth at the same time) and the full-duplex nature of the telephonyenvironment. The present invention uses a signal processing algorithm ofthe type referred to as voice modulation recognition or voice detectionto activate the transmitter to ensure that the transmitter will onlytransmit when the party on the telephony network is speaking, and willnot transmit due to background noise or other non-speech signals. Suchan algorithm in a Radio-to-SIP interface is unique and provides a highlyeffective method of connecting half-duplex communication devices to aSIP telephony network. The radio appears as any other SIP end point andthe user requires no training and is not required to push a specifiedkey on a telephone keypad to activate the transmitter as some systemsmay require.

Referring now to FIG. 1, a radio-to-SIP adapter 10 is shown to include avoice detection algorithm processor 12 as well as other circuitry (notshown) to provide an interface between a radio and SIP adapter. Itshould be appreciated the radio-to-SIP adapter 10 can be a stand aloneunit or included as part of an SIP adapter during manufacturing of theSIP adapter. The radio-to-SIP adapter 10 includes an audio signal input14 which also provided as an output 16. The audio input signal includesthe audio that is to be tested for the presence of human speech. Theradio-to-SIP adapter 10 also includes a radio transmit signal output 18.The radio transmit signal provides an indication to the radio that theradio is to enable its transmitter and transmit audio.

The radio-to-SIP adapter 10 is disposed between the local radio and theSIP adapter that provides an interface into the IP network that theVoice over IP communication application is operating.

Referring now to FIG. 2, a flow chart 100 is shown describing theoperation of the radio-to-SIP adapter 10 starting at step 22. As shownin step 24, the radio-to-SIP adapter monitors the audio signal input 14for audio and processes the audio through the voice detection algorithmprocessor 12 to detect the presence of human speech in the audio signal.As shown in step 26, if human speech is detected, the radio-to-SIPadapter 10 sets the radio transmit signal to active so the that radiowill turn on its transmitter and transmit audio, otherwise theradio-to-SIP adapter 10 sets the radio transmit to inactive. As shown instep 28, steps 24 and 26 are repeated in real time so that the radiotransmit signal remains in sync with the audio signal.

It should be appreciated that a flowchart represents computer softwareinstructions or groups of instructions. Alternatively, the processingand decision blocks represent steps performed by functionally equivalentcircuits such as a digital signal processor circuit or an applicationspecific integrated circuit (ASIC). The flow diagrams do not depict thesyntax of any particular programming language. Rather, the flow diagramsillustrate the functional information one of ordinary skill in the artrequires to fabricate circuits or to generate computer software toperform the processing required of the particular apparatus. It shouldbe noted that many routine program elements, such as initialization ofloops and variables and the use of temporary variables are not shown. Itwill be appreciated by those of ordinary skill in the art that unlessotherwise indicated herein, the particular sequence of steps describedis illustrative only and can be varied without departing from the spiritof the invention. Thus, unless otherwise stated the steps describedbelow are unordered meaning that, when possible, the steps can beperformed in any convenient or desirable order.

The voice detection algorithm performed by the processor 12 can be anyvoice detection algorithm that can detect human speech. For example, aone example of a voice detection algorithm that can detect human speechhas been implemented using a Texas Instrument TMS320VC5409 digitalsignal processor. It should be noted, unlike a speech recognition devicewhere speech is being analyzed to convert speech to text, in the presentdevice the audio is being analyzed to detect the presence of humanspeech.

Referring now to FIG. 3, a block diagram of a voice detection algorithm40 implemented by software in processor 12 is shown to include an audioinput 42. The audio is segregated by a plurality of band pass filters 44into a plurality of signals 45 a, 45 b, 45 c, 45 d having variousfrequencies within each of the respective bandwidths. Each one of theplurality of signals 45 a-45 d are fed into a respective one of theenvelope detectors 45 where such signals are averaged. Each one of theoutput signals 47 a, 47 b, 47 c, 47 d are fed into a respective one of aplurality of low pass filters 48. Each one of the output signals 49 a,49 b, 49 c, 49 d are fed into a respective one of a plurality ofenvelope detectors 50 where such signals are averaged. Each one of theoutput signals 51 a, 51 b, 51 c, 51 d are fed into syllabic detectiondecision logic 52 where the various time and amplitude thresholds of thesignals fed into the syllabic detection decision logic 52 are used todetermine the presence of human speech as learned from prior known humanspeech. The latter will recognize the presence of speech in the midst ofother sounds such as radio static and background noise. When thepresence of human speech is detected, a speech detect signal 54 isprovided to activate the radio as appropriate.

It should now be appreciated the radio-to-SIP adapter 10 monitors theaudio signal from the telephony network and activates the radiotransmitter when the radio-to-SIP adapter 10 detects human speech.

Having described the preferred embodiment of the invention, it will nowbecome apparent to one of ordinary skill in the art that otherembodiments incorporating their concepts may be used. It is felttherefore that these embodiments should not be limited to disclosedembodiments but rather should be limited only by the spirit and scope ofthe appended claims.

1. A radio-to-SIP adapter comprising: a voice detection algorithmprocessor to detect the presence of human speech in an audio signal; anaudio input to receive an audio signal; and a radio transmit indicatorsignal output to provide a signal to indicate that human speech ispresent in the audio signal.
 2. The radio-to-SIP adapter as recited inclaim 1 wherein the radio-to-SIP adapter is integrated with a SIPadapter.
 3. The radio-to-SIP adapter as recited in claim 1 wherein thevoice detection algorithm processor comprises a Texas InstrumentTMS320VC5409 digital signal processor.
 4. A method to cause a radio totransmit comprising: monitoring an audio signal and processing saidsignal with a voice detection algorithm to detect the presence of humanspeech in the audio signal; activating a radio transmit signal if humanspeech is detected to cause a radio to transmit audio; and deactivatinga radio transmit signal if human speech is not detected to cause a radionot to transmit audio.
 5. The method as recited in claim 3 wherein theaudio signal is from a telephony network and the method is repeated toremain in sync with the human speech in the audio signal.
 6. Aradio-to-SIP adapter comprising: a voice detection algorithm processorto detect the presence of human speech in an audio signal; an audioinput to receive an audio signal from a telephony network; a radiotransmit indicator signal output to provide a signal to indicate thathuman speech is present in the audio signal and to cause a radio totransmit audio when human speech is present in the audio signal from thetelephony network.